With the popularity of ultra-high resolution video pictures in the market, video and image codecs increase a bandwidth burden to an external memory, and a large amount of data exchanges with external memories also increase power consumption of a chip. Video data compression is a way to solve the problem of bandwidth burden. There are generally three picture compression methods: lossy compression, lossless compression and hybrid compression consisting of lossy and lossless compression. Lossy compression generally employs a method of quantizing the data to be compressed. Lossless picture compression usually has two stages: prediction and entropy coding. The processing method at the first stage generally includes two types. One is prediction processing, e.g. spatial prediction, which is utilized to get a difference between data to be compressed and a predicted value, and then the second stage of processing will be performed. The other is transform processing, which is utilized to transform the data to be compressed to the frequency domain, and then the second stage of processing will be performed. The processing method at the second stage is usually entropy coding processing, in which variable length codes are typically used in encoding to achieve data compression.
Lossy compression typically yields an increase in compression rate at the expense of loss of video visual quality, which may lead to degraded visual quality of a current video picture. However, if the current video picture is used by the video encoder and decoders as a reference video picture for the subsequent video pictures, the quality loss of the current video picture may propagate to the subsequent video pictures, which further degrades the quality of the sequence of video pictures. Although the lossless compression may not degrade the quality of the video pictures, its data compression rate is low for video sequences with complex textures, and thus is not suitable for applications with relatively limited external memory bandwidth and footprint budgets.
Therefore, it is desirable to improve the existing methods of video data compression.